Hydraulic brake



Aug. 14,' W STELZER v 2,382,268

HYDRAULIC BRAKE FiledOCt. l5, 1942 5 Sheets-*Sheet l INVENTOR.

` yAug'.14, 1945. w. sTELzl-:R y 2,382,268

HYDRAULIC BRAKE Filed Oct. 15, 1942 3 Sheets-Sheet 3 IN VEN TOR.

leasing means to prevent Patented Aug. 14, 1945 UNITED STATES PATENT OFFICE HYDRAULIC BRAKE william stelzer, Detroit, Mich.

Application` October 15, 1942, Serial No. 462,067

(Cl. 18s-152) 3 Claims.

The invention relates to hydraulic brakes and more particularly to a torque-responsive hydraulic brake for vehicles where the brake torque is utilized to provide a booster action and where the pedal feel is proportionate to the braking effect.

In devising present day boosters for hydraulic brakes it has been the aim to obtain a construction where the effort to expand the brake shoes is in a constant and pre-determined proportion to the eii'ort exerted by the operator on the brake pedal in order to obtain a desired pedal feel." While a certain modulation is thereby obtained it does not take into account the eiect of the brakes. Assuming that one brake is dry, and another wet, or that one brake is more or less effective'for one reason or another, a very serious unbalance may result even though the brakes are inherently equalized due to the hydraulic operation, which unbalance is frequently the cause of accidents.

The object of my invention is a departure from the conventional requirement, to obtain a brake where the pedal pressure is in proportion to the braking effect, and where not the force to expand the brake shoes, but the braking effect is equalized.

Another object is to obtain a construction where the brake torque is utilized to create a booster action to reduce the necessary exertion by the operator.

A further object of the invention is to eliminate the danger of a grabbingbrake caused by variations in the coeilicient of friction of the brake linings, by providing a construction where the shoes are automatically released-until the brake torque is equal to that in the other wheels of the vehicle.

It is also the aim of this invention to effect an eilicient booster action inherent in the brake itself, and without the help of intricate and expensive booster mechanisms which require a special source of power; An important aim is to simplify the construction of hydraulic brakes and to thereby reduce.

dependability and usefulness.

Yet another aim isto provide automatic reg of the brakes andto enable the use of self-energizing brake shoes which provide a booster action.

Other objects and advantages of this invention will be apparent from the following detailed description considered in connection with the accompanying drawings submitted'for the purpose o1' illustration and not to define the scope of the the cost of manufacturing and to increase their invention, reference being had for that purpose to the subjoined claims. In the drawings, wherein similar reference characters refer t0 similar parts throughout the several views:

Fig. 1 is a side elevation of a brake built according to the novel principle, where the wheel cylinder is shown in section, and where the wheel is removed to provide an unencumbered view of the brake actuating elements;

Fig. 2, is a diagram to show the connection between a plurality of wheel cylinders;

Fig. 3, a side elevation partly in section of a modified brake: and

Fig. 4, a side elevation partly in section showing a further modification.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being.

practised or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not for limitation.

Describing the invention now in detail, thereis shown a brake arrangement for a wheel of a vehicle, where l designates the usual backing plate to which the various non-rotating elements are attached, and Z'represents the brake drum which revolves with the wheel. Secured to the backing plate is a wheel cylinder or brake actuator 3 in which slide pistons- I and 5 having piston seals 6 held in contact with said -pistons by a spring I in chamber 8, the latter being in communication with the master cylinder or other pressure producing device through a brake line 9. Pistons 4 and 5 have piston rods I0 and II engaging lever I2` and brake shoe I3 respectively. Piston rod II has a cap I4 attached thereto serving as stop in the retracted or "ofP position. Piston rod III carries a seal I5. 'I'he wheel cylinder is shown only diagraminatically, such conventional parts as dust covers, adjusting members for brake wear, and bleeding devices, being left on in order to illustrate the invention more clearly. Lever I2 is fulcrumed on an anchorage pin IB attachedto the backing plate, and 'rests against a solid stop I'I- alsoextending from back-V ing plate I. Brake shoe I8 engages lever I2 `at I9. Both brake shoes are hinged together at 20 so that nothing prevents them from rotating except: lever- I2 and cap I4. The contractile movement of said brake shoes is limited by stop pins 2| extending from backing plate I, whereby 'a brake shoes are held a certain distance from the brake drum by retraction springs 22.

While the embodiment described is suitable `where a booster eilect is required primarily ior forward travel, in vehicles where the brakes should be equally eilective when going backwards, the modified brake shown in Fig. 3 may be used.

In the entirely symmetrical arrangement the wheel cylinder 23 attached to backing plate I has pistons 24 whose piston rods 25 are lguided to slide in end caps 26 secured to wheel cylinder 23.

Piston rods 25 engage levers 21 pivoted at 28 to shoes 29 and at their other extremity resting Vintermediate the two brake shoes and engages them on the surface between points 35 and 36.

The same principle illustrated in Fig. 3 is carried out by hydraulic means in Fig. 4. In this embodiment cylinder 31 contains pistons 38 resting against end caps 39 and within which slide,

smaller'pistons 40 having shoulders AIII to abut against pistons 38 provided with seals 42 serving both the'large and small pistons. A spring 43 holds them in engagement. I'he piston rods 44 of pistons 40 contact brake shoe 45 whose web is smaller in section to give it suiilcient elasticity to be capable of expanding to contact the brake drum during a brake application.

Having thus described the invention, I shall now explain the operation of the'same. All the views show the oi or released position. The braking systems usually consist of a plurality of wheel cylinders, and a master cylinder or other fluid pressure producing device 46, connected as illustrated in Fig. 2.

Assuming that the operator depresses the brake pedal to apply the brakes, a pressure is produced in chamber 8, reference being had to Fig. 1. Since lever I2 rests against stop pin I1,y only piston 5 is able'to move, pushing the tip of brake shoe I3 against brakev drum 2 revolving in the direction indicated by arrow 41.. As soon as brake shoe I3 is brought into contact with the brake drum, the brake torque resulting from the friction between the brake shoes and the rotating drum is transmitted to react against lever I2 at point I9. Lever I2 in turn transmits the brake torque to act on piston 4 through piston rod l0. The force acting on lever vI2 includes the force of application produced by piston 5. It will be seen that due tothe ratio oflever I2 the force acting on point I9 must exceeds, certain multiple of the hydraulic pressure in chamber 8 before piston 4 is forced into cylinder 3 to displace uid in chamber 8, said. fluid displaced being transmitted to further apply piston either in the same brake or in the other brakes of the vehicle. -It is thus obvious that the proportion of lever I2 governs the booster ratio of the brake. While the booster -ratio is governed by lever I2, the boosting action itself is produced by the friction members I3 and I 8, receiving the energy from the rotating brake drum 2.. If thefriction of brake shoes I3 and I3 is small for one reason or another, as for instance'due to a glazing of the friction surfaces,

or due to dirt or grease, the brake torque produced may not be sumcient to moveilever I2, but

brake shoes the brake action is allowed to build'` due to the self-energizing or servo-action o! the Vvtioned, that piston breaches the end of its stroke Vbefore lever I2 touches cylinder 3. This is necessary because arresting of lever I2 would defeat the modulating action of the brake. After piston 5' is seated on the bottom of cylinder 3, piston 4 continues to hold the brake in engagement, where the brake acts as an unwrapping brake and the torque is transmitted partly to oppose the hydraulic iluid in chamber 8 and partly to pivot pin I6. In this position any grabbing of the brake or increase in the braking effect that is not the result of an increased manual effort to apply the brakes, causes brake shoe I3 to break away from piston rodv II, whereby the servo-ac tion and with vit the braking effect is 'immediately reduced, until the latter is in a pre-determinedproportion to the hydraulic pressure orv manual brake effort. Thus it is apparent that lever I2 in combination with piston 4 serves 'as a brake torque relieving means to keep the brake torque in a pre-determined relation to the operating pressure .of the hydraulic iluid, or to limit the braking effect so that it is in proportion to the braking eiort. Supposing now that the opfrs,

eratorreleases the brake pedal, theV hydraulic pressure in chamber' 8 is relieved, whereby the concerted eilort of springs 22 retract the brake shoes to the olf position-as shown in Fig. 1, where the brake shoes are disengaged from the drum.

When the brake is applied while the vehicle is going backwardly, it is less effective becausejthe brake torque opposes piston 5, while piston 4 re-` mains idle because lever I2 rests against stop I1. In the construction in Fig. 3 the operation is similar to that of the construction Just described, except that the operation is`l the same for iorward or backward travel of the vehicle, because the construction is entirelyfsymmetrical'.`

supposing a, hydraulic pressure is produced y'in chamber 8 by a pressure producing/ device such as master cylinder 46 operated by the operator, pistons 24 are pushed apart to bring the brake shoes 29'into contact with the brake drum 2. Levers 21 abutting against points 3i serve only as intermediate members to transmit the force of application directly to the brake shoes. As soon as the latter come into contact with the rotating brake drum a brake torque is'produced urgingl brake drum 2.

For this example, it is assumed thatthe rotation of the brake drum is clockwise as viewed on the drawings. The elements arranged symmetrically will be referredto as right or left. 'I'he right hand brake shoe, by revolving a short distance with said brake drum, pushes the lower extremity of link or lever 33 towards the left so that it pivots about anchor pin 34 and advances the left brake shoe in a clockwise rotation but at a faster pace than that of the right shoe, because the latter engages link- 33 at 35, whereas the left shoe is engaged at 3 6. where the travel is greater. Thus link' 33 provides a certainf booster action because by virtue of ,-its'tunctionthe left hand piston' 24 travels faster'tol the right to enter cylinder!` 23" pushing piaff ratio for a smaller braking eiTect.

.assaaos l l until shoulder 4| comes to rest against cap 3l.'

than the right hand piston which moves also to the right. The pace of the left hand piston 24 is further speeded up as soon as the lower extremity of the left lever 21 stops against anchor pin 30 and point 3| loses contact with lever 21. 'I'he brake actuating mechanism is so proportioned that the right hand piston bottoms against cap 26 before lever 21 on the left side touches the left cap The same is true in the opposite direction. Supposing that the brake torque is suiiicient to overcome the resistance offered by the hydraulic fluid under pressure in chamber 8, the movement of pistons 24 -continues until the right hand piston rests against cap 2B. Further movement of the right hand shoe would result in the release of the brake shoes and consequent relief of the brake torque. It is therefore obvious that the brake torque cannot increase unless the hydraulic operating pressure is increased proportionately.

It will be observed that anchor studs 30 are oblong in shape. This is intended to provide a change in leverage in levers 21 whereby the-lever ratio increases while approaching cap 26. This feature results in a greater booster ratio for a maximum braking effect, and a smaller booster l Since the booster ratio is on an increasing scale the mechanismv may come to an equilibrium before the right 0n the left hand side the brake shoe continues to act on piston 40 and Il but further advance into cylinder I1 is stopped because any advance causes shoe 45 to move away from piston rod 44 at the right hand side. thus releasing the brake shoe, with a resultant decrease in brake torque which is immediately overpowered by the hydraulic pressure in chamber 8, so that the shoe at the right hand side becomes engaged again with piston .rod 44` and the shoe (is pressed harder against the brake drum. The brake mechanism assumes a balanced or holding position where shoulder 4l rests against piston 28 with a variable pressure. Thelatter is high if the coeiliclent of friction of the friction member 45 is high, and low if its coemcient of friction is low. In the la-tter case, a greater force is applied to the right hand tip of the brake shoe. When the operator releases the brake pedal and the operating pressure in chamber 8 drops,

yspring 22 as well as the inherent resiliency of shoe 45l contract the latter to assume the off position determined by stop pins 2|. Furthermore, the tips of the shoe are equidistanced from .cylinder I1 by virtue of spring 42.

It is apparent that the function is similar to that described when the brake drum revolves counterclockwise.

hand piston comes to re's't against cap 26, unless the coemcient of friction reaches a value above average.

supposing now that the operator releases the brake pedal and that the hydraulic operating pres- -sure is therefore relieved, springs 22 immediatelyv retract shoes 29 so that they rest against locating pins 2l. Link 33 during the retractile movement serves as an automatic centering means because spring 22 tends to pull the shoes together to a position where the distance between them is shortest', which is the case when link 33 is in a central position and all points and 36 are bearing.

It is logical that the function is similar to that described when brake drum 2 is revolving in the opposite direction, because the construction is symmetrical.

Describing the operation of the construction shown in Fig. 4. itis again assumed that the brake While the motive fluid preferably consists of hydraulic brake fluid, compressed air or any other suitable agent may be used.

The invention may also be applied to other devices, as for instance to clutches, or transmission brakes.

I claim: f l. A brake comprising a revolving member to turn with a wheel, a pair of brake shoes arranged to engage said revolving member during a brake application, a hydraulic actuator cylinder intermediate said brake shoes, hydraulic fluid to operate said actuator, manual means to put said hydraulic fluid under pressure, a pair of opposed pistons in said actuator cylinder, a lever intermediate leach shoe `and piston and operative in response to the brake torque, said lever being of the two arm type where the brake torque acts drum revolves in a clockwise rotation. When the y `rod 44 at the left, .causing the left hand piston 4Ii to move to the right, i. e., to enter chamber 8 until shoulder 4I abuts against the left piston 28. Further movement to the right is resisted by the fluid pressureacting on piston 28. If the coeiiicient of friction oi the brake shoe is high, resulting in a higher brake, torque, piston 38 is overpowered sothat on the left side pistons 40 and 38 move to enter chamber 8 in unison, and on the "right hand side piston 40 moves out' of the cylinder hydraulic operating pressure is applied to engage y 5o other end of said lever, and means to render said against said lever at an intermediate point and is opposed by one of said pistons acting at one end of said lever and by a iixed reaction point at the said levers are arranged to restV against said brake shoes after the force exerted by said brake shoes on said intermediate point yields to the force ex erted by said pistons.

3. The commotion as claimed-in claim 1 where ,o said fixed reaction point is onan anchor member l yields.

where'tne point of contact between said lever and said anchor member changes with the position of said lever to provide an increasing leverratio, whereby said lever ratio increases as said piston .WILLIMGISTELZER. 

